The invention relates to a device for the feeding of material bars for processing machines, with which in a tube the rearward end of the bar is moved in the direction of the processing machine by a piston guided in the tube and loaded by a pressurising medium.
Devices of the above-mentioned type are already known, with which a piston guided in the tube moves the bar to be machined in the direction of the processing machine. The tube here has the function of a cylinder, that is, the volume of the tube behind the piston is loaded by a pressurising medium, for instance compressed air or hydraulic oil. It is a disadvantage with these known devices that the piston must be satisfactorily guided over a considerable length in the tube, in order to keep leakage losses of the pressurising medium as small as possible. This is virtually impossible with considerable tube lengths. Also if the tube is damaged or distorted a satisfactory guidance of the piston within the tube is no longer ensured. Consequently in the case of long tubes use is primarily made of a weight feed, where the piston is fixed to a cable which is led over turning rollers and carries a weight on its end. This again necessitates the tube being slotted over its entire length.
Another disadvantage of the known devices resides in the fact that the tube diameter has to be matched to the diameter of the material bar to be machined. The rotating bar of material, guided by the piston in the direction towards the processing machine, sags, which leads to it being caused to vibrate, and these vibrations are transmitted to the entire bar feeding device and the processing machine. Through an appropriate choice of the tube diameter it is possible to hold the amplitude of the vibrations within limits. This however leads to wear phonomena which again affect the satisfactory gudance of the piston in the tube. Moreover an unpleasant noise results from the contact between bar and tube, which can only be reduced by expensive external damping measures.
The problem exists so as to constitute the bar feeding device that a satisfactory guidance of the piston in the tube is possible without losses of the pressurised medium through leakage and the vabrations of the bar referred to above are avoided.